The field of art to which this invention pertains is the selective hydrogenation of olefins contained in a hydrocarbon stream comprising olefins and aromatic compounds. Hydrogenation processes have been used by petroleum refiners and petrochemical producers to produce more valuable hydrocarbonaceous products. Hydrocarbonaceous streams containing olefins and aromatic compounds are only useful if the olefins can be selectively hydrogenated without the simultaneous hydrogenation of the aromatic compounds. Previously, selective hydrogenation has been performed with a supported catalyst containing metals including those of Group VIII with particular reference to nickel. However, nickel catalysts are not sufficiently selective because they have a marked tendency to hydrogenate a significant part of the aromatic compounds when selectively hydrogenating olefins. The selectivity is not satisfactorily improved even when the hydrogenation operations are performed at low pressures of approximately 30 to 50 bar and at low temperatures between 50° C. (22° F.) and 180° C. (356° F.). The prior art has taught that the selectivity of these catalysts can be improved by injecting sulfur compounds prior to the contacting of the catalyst and the reactive feedstock.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in the selective hydrogenation of olefinic hydrocarbons, there is always a demand for new selective hydrogenation methods which provide lower costs and the required product quality.